Fuel supply systems for engines

ABSTRACT

A fuel system for an engine has control means determining the rate of supply of fuel to the engine. This control means is responsive to system parameters, one of which is obtained from a demand transducer. The minimum speed of the engine is limited in accordance with the rate of supply of fuel to be produce an idling curve having a predetermined slope, and this slope is increased if the engine speed is below a predetermined value.

United States Patent Williams et al.

[ 1 Aug. 12, 1975 FUEL SUPPLY SYSTEMS FOR ENGINES Inventors: MalcolmWilliams, Solihull;

Christopher Robin Jones, Alcester; Richard William Crookes, Solihull,all of England C.A.V. Limited, Birmingham, England Filed: Dec. 28, 1973Appl. No.: 429,373

Assignee:

Foreign Application Priority Data Jan. 6, 1973 United Kingdom 890/73 US.Cl. 123/139 E; 123/140 R; 290/40 A; 60/3928 Int. Cl. F02!) 3/00; F02m39/00 Field of Search 123/102, 139 E, 32 EA, 123/140 R; 290/40 A;60/3928 References Cited UNITED STATES PATENTS 10/1968 Lang 123/139 E3,425,401 Z/l969 Lang 123/139 E 3,693,603 9/1972 Lemawczyk.. 123/139 E 3699,935 10/1972 Adler 123/139 E Primary Examiner-Charles J. MyhreAssistant Examiner-Ronald B. Cox Attorney, Agent, or FirmHolman & Stern3 Claims, 5 Drawing Figures PUMP 3 OUTPUT Q SPEED PATENTEU 3,898,969

SHEET 1 ACTUATOR PUMP ENGINE DRIVE 23 44 H SPEED CIRCUIT 5 /TRANSDUCER IPEDAL POSITION I TRANSDUCER MAXIMUM $258355? 27 A5 @555? /---#SOURCE 2925 2b 24 {8\ CURRENT SOURCE Z2\ Ho 21 u u 53 55 g 52 SOURCE-\\ PATENTED3,898,969

SHEET 2 W PEDAL osmow SPEED PUMP OUTPUT- FIG. 2. FIG. 3). F154.

PUMP OUTPUT FUEL SUPPLY SYSTEMS FOR ENGINES This invention relates tofuel systems for engines, particularly, but not exclusively,compression-ignition engines.

A system according to the invention includes control means determiningthe rate of supply of fuel to the system, a demand transducer providingan input to the control means to influence the output thereof, means forlimiting the minimum speed of the engine in accordance with the rate ofsupply of fuel to produce an idling curve having a predetermined slope,and means for increasing the slope of the idling curve when the enginespeed is below a predetermined value.

Preferably, the means for increasing the slope supplements the input tothe control means from the demand transducer, so as to simulate anincreased demand.

The accompanying drawings illustrate one example of the invention asapplied to a fuel injection system for a diesel engine driving a roadvehicle. In the drawings,

FIG. 1 is a circuit diagram, partly in block form, of the system FIGS. 2to 4 respectively illustrate the outputs of three transducers used inthe system, and

FIG. 5 represents a fuelspeed characteristic for an engine to becontrolled by the arrangement of FIGS. 1 to 4.

Referring first to FIG. 1, a pump 11 provides fuel to an engine 12, therate of supply of fuel being determined by a control rod 13 forming partof the pump 11, and the position of which is determined by a actuator14. The control rod 13 is loaded by a spring to a position in which thepump 11 produces a Zero output, and the actuator 14 moves the controlrod 13 against the action of the spring to increase the output of thepump 1 1.

The rotational speed of the engine 12 is sensed by a transducer 15 whichproduces an output voltage of the form indicated in FIG. 2, this outputvoltage being at a maximum when the engine speed is low. The transducer15 provides a current input by way of a resistor 16 to the invertingterminal of an operational amplifier 17 which receives its power from apair of terminals 18, 19 and has its non-inverting terminal connected toa terminal 21. The terminal 18 is positive with respect to the terminal19, and the terminal 21 is at a potential mid-way between the potentialsof the terminals 18, 19. The origin in FIGS. 2 to 4 represents thepotential of the terminal 21. The output from the amplifier 17 is fedthrough a diode 22 to the input terminal ofa drive circuit 23 operatingthe actuator 14. The amplifier 17 also receives input from a currentsource 24 which sets the minimum speed of the engine and by way of apair of resistors 25, 26 respectively from a pair of transducers 27, 28.The transducer 27 senses the pump output by detecting the position ofthe control rod 13, and produces an output voltage of the form shown inFIG. 3. The transducer 28 is operable by the pedal of the road vehicle.and produces an output voltage representing demand, this voltage beingof the form shown in FIG. 4. The operational amplifier 17 is connectedas a summing amplifier, and for this purpose has a feedback resistor 29which is connected between the input of the drive circuit 23 and theinverting terminal of the amplifier 17.

There is further provided an operational amplifier 31 the invertingterminal of which receives a signal by way of a resistor 32 from thetransducer 27, and also receives a signal from a current source 33 usedto set the maximum pump output. The output from the amplifier 31 is fedthrough a diode 33 to the drive circuit 23, and feedback to theinverting terminal of the amplifier 31 is taken by way of a resistor 34from the input of the drive circuit 23.

Ignoring for the moment the components shown in the lower half of FIG.1, the operation of the system is best explained with reference to FIG.5. The line 41 in FIG. 5 is one of a family of curves representingengine demand, and for the sake of convenience can be said to represent50 percent maximum speed. If the pedal is set to the 50 percentposition, then it provides an input to the amplifier l7, and this inputis compared with the actual speed signal by way of the resistor 16. Ifthere were no input from the transducer 27, then the amplifier 17 wouldsimply compare the demanded speed with the actual speed, and operate thedrive circuit 23 to cause the actuator 14 to move the control rod 13 tovary the pump output until the actual and desired speeds were equal.However, by virtue of the signal through the resistor 25 representingpump output, the slope shown on the curve 41 in FIG. 5 is obtained. Inother words, for a 50 percent demand, the position of the engine on thecurve 41 will depend on the pump output, so that there is a range ofspeeds for a 50% demand, dependent upon the load on the engine.

It will be seen that whenever the amplifier 17 is producing a positiveoutput which is greater than the output of the amplifier 31, the diode33 is reverse biased so that the amplifier 31 plays no part in theoperation. The purpose of the amplifier 31 is to limit the maximum pumpoutput, as indicated by the curve 42 in FIG.

- 5. If at any time the maximum pump output reaches the curve 42, thenby virtue of the current source 33 and the connection through resistor32, the amplifier 31 produces an output which is a greater positiveoutput than the output produced by the amplifier 17, so that the diode22 is now reverse biased, and the amplifier 31 provides an input to thedrive circuit 23. Although the output from the amplifier 31 is a largerpositive output than the output from the amplifier 17, this actuallyrepresents a demand for less fuel, and so the fuel is regulated in sucha way that the pump output does not exceed the quantity indicated by thecurve 42.

As previously explained, the curve 41 is one of a family of curvesrepresenting different demands. The zero demand curve is shown, partlydotted, at 43, and is set by the current source 24 so that, ignoring thelower part of FIG. 1, the minimum speed follows the curve 43. Themaximum speed of the engine is indicated by the curve 44, and is set bya source 45 which acts by limiting the maximum demand of the demandtransducer 28.

The dotted curve 46 shown in FIG. 5 is a function of the engine, not thecontrol system, and represents the no-load idling speed of the engine.As will be seen, the no-load zero demand operating point is the point 47in FIG. 5.

With the arrangement thus far described, the engine will operate at thepoint 47 during no-load idling. However, if a load is imposed on theengine in these circum stances, the engine speed falls substantially asshown by the dotted portion of the curve 43. This substantial possiblechange in speed at zero demand can result in an undesirable jerk, and insome cases stalling of the engine. The problem occurs particularly onvehicles with automatic transmission, where engagement of thetransmission with the vehicle at rest and no demand imposed by the pedalwill result in an increase in load.

In order to overcome this difficulty the slope of the curve 43 isincreased below a predetermined speed, as shown by the solid line 43a.As a result, the change in speed with load is substantially reduced. Thepredetermined speed will depend on the engine, and need not be the point47. The change in slope is achieved by effectively applying to theinverting terminal of the amplifier 17 a further current simulating apredetermined demand, this signal being applied to the amplifier 17 onlywhen the engine speed falls below the predetermined speed. For thispurpose, the transducer provides an input to the base of an n-p-ntransistor 51, the collector of which is connected through a resistor 52and a diode 53 in series to the terminal 18, and the emitter of which isconnected to the terminal 19 through resistors 54, 55 in series. Asecond n-p-n transistor 56 has its collector connected through aresistor 57 to the terminal 18, and its emitter connected to theterminal 19 through a resistor 58 and the resistor 55 in series. Thebase of the transistor 56 is connected through a resistor 59 to theterminal 18, and through a resistor 61 to the terminal 19. The collectorof the transistor 51 is connected to the base of a p-n-p transistor 64having its emitter connected through a resistor 65 to the collector ofthe transistor 56 and its collector connected to the inverting terminalof the amplifier 17. As previously explained with reference to FIG. 2,the transducer 15 produces its greatest output when the engine speed isat a minimum value. At high speeds, the output voltage of the transducer15 is insufficient to turn on the transistor 51, and the transistors 56,64 are off. With decreasing speed, the long tailed pair 51, 56 share thecurrent flow in the resistor 55, until at the predetermined speed thetransistors 51, 56 are conducting equally and the transistor 64 is offbut about to conduct. Any further decrease in speed causes thetransistor 56 to conduct more than the transistor 51, so that thetransistor 64 conducts to supplement the current flowing to theinverting terminal of the amplifier 17, so producing the line 43a inFIG. 6. The resistor 64 is used to set the slope of the line 43a, andthe resistor 61 to set the predetermined speed. The arrangement usedminimises drift with, for example, temperature in the predeterminedspeed, and in particular the diode 53 balances the base-emitter diode ofthe transistor 64.

The arrangement shown is an all speed governor, but

the invention can be applied to other forms of governor. For example,the invention could be applied to a two-speed governor in which theamplifier 17 com pares the pump output with a demand signal derived fromthe pedal, and representing the desired pump output. In this case, theinput through the resistor 16 to the amplifier 17 is not required. Thetransducer 15 now provides a current input to the amplifier 31, whichserves in this case to limit the maximum speed. The signal from thetransducer 27 is still fed to the amplifier 31 so that the maximum speedis dependent upon pump output as indicated by the slope of the curve 44in FIG. 5. The source 45 in this example is provided with a signal fromthe transducer 15 and is used to set the maximum pump output, and thesource 24 would require an input from the transducer 15 so that itsoutput is speeddependent to give the required slope of the curve 43. Theoutput from the transistor 64 is still applied to the amplifier 17 inthis arrangement, and has basically the same effect.

We claim:

1. A fuel supply system for an engine, including control means fordetermining the rate of fuel supply by the system, a demand transducerfor providing a signal to the control means representing a demandedengine operating parameter thereby defining engine operating curveshaving a first predetermined slope, means for limiting the minimum speedof the engine in accordance with the rate of supply of fuel to producean engine idling curve of a second predetermined slope less steep thansaid first predetermined slope, and means operable when the engine speedfalls below a predetermined value for supplementing the input applied tothe control means by the demand transducer so as to simulate anincreased demand and produce an engine idling curve having a thirdpredetermined slope steeper than said first predetermined slope.

2. A fuel supply system as defined in claim 1, wherein said thirdpredetermined slope is substantially vertical thereby effecting asubstantially maximum rate of fuel supply to the engine when said enginespeed falls below said predetermined value.

3. A system as claimed in claim 2 in which the control means comprises apump supplying fuel to the engine, an actuator controlling the output ofthe pump, and an electronic governor controlling the actuator, thegovernor receiving an input from the demand transducer and from at leastone further transducer responsive to a sys-

1. A fuel supply system for an engine, including control means fordetermining the rate of fuel supply by the system, a demand transducerfor providing a signal to the control means representing a demandedengine operating parameter thereby defining engIne operating curveshaving a first predetermined slope, means for limiting the minimum speedof the engine in accordance with the rate of supply of fuel to producean engine idling curve of a second predetermined slope less steep thansaid first predetermined slope, and means operable when the engine speedfalls below a predetermined value for supplementing the input applied tothe control means by the demand transducer so as to simulate anincreased demand and produce an engine idling curve having a thirdpredetermined slope steeper than said first predetermined slope.
 2. Afueld supply system as defined in claim 1, wherein said thirdpredetermined slope is substantially vertical thereby effecting asubstantially maximum rate of fuel supply to the engine when said enginespeed falls below said predetermined value.
 3. A system as claimed inclaim 2 in which the control means comprises a pump supplying fuel tothe engine, an actuator controlling the output of the pump, and anelectronic governor controlling the actuator, the governor receiving aninput from the demand transducer and from at least one furthertransducer responsive to a system parameter.